Go with that. AC2 and AC:R combine for less than 1500 players on Steam, Brotherhood isn't even listed. Skyrim has 80,000. Have fun disagreeing with fact.

Skyrim is a Steamworks game, so pretty much everyone who bought it shows up on the Steam count. The AC games aren't Steamworks games, so only the people who bought the games through Steam show up on the Steam count. Granted, I've little doubt Skyrim has far more people playing than all the AC games combined anyway, but using Steams numbers isn't a fair comparison.